The present invention relates to a method and apparatus for processing image data for transmission along telephone lines and for decoding the processed data after transmission such that the data can be transformed to produce color images of color television quality.
Known systems for transmitting image data along telephone lines are severely limited in the speed at which the data can be transmitted and reassembled at a receiving end. For example, a single frame of a color television quality image contains 512 by 512 by 24 bits and takes approximately 90 seconds to transmit without compression using a 64 kilobit per second standard ISDN B channel. One method to enhance transmission speed is to compress the data according to known transforms and then, after transmission, to decompress the compressed, transmitted data.
A television screen, for example, is divided up into a plurality of individual image units referred to as pixels. For colour images each pixel may contain three separate parameters such as red, green and blue. Each parameter may be defined as to intensity by an eight bit number called a byte. Thus, each pixel is defined by three bytes. In order to process the data efficiently it is useful to treat a block of 8 by 8 pixels known as a "tile". A known technique consists of directing a first tile of an image into a processor and then inputting the first tile into a digital transformer. The tile output modified by the transformer is sent back to the processor where it is further compressed and sent to an output port. The second tile in the image is then sent to the transformer. This process is repeated until all of the image tile have been processed. In such a system the requirement for numerous fetch and other instructions from the processor makes the process impractically slow. Thus, the advantages of transmission speed increase due to compression is offset by the time take to compress and decompress.
Accordingly, it is an object of the invention to provide an improved method of processing imaging data for compression and decompression. It is a further object of the invention to provide a buffer to receive and store data corresponding to an image and then to process the captured data.